[FOSS-GPS] Questions regarding NV08C-CMS + RTKLIB

Danny Miller dannym at austin.rr.com
Sun Nov 3 13:55:10 PST 2013

I have a pair of the NV08C.  It's a great module.

A couple of things:
The NV08C has both a powered and passive antenna mode (the TW3430 is 
powered).  Mixing them up causes signal level problems.  Also an 
external cap is required for passive antenna mode but cannot be there 
for powered-antenna mode.

Also check that the NV08C can provide the 16ma needed by the TW3430.

Don't try to use GLONASS.  IIRC there's problems with channel 
calibrations on those.

It is entirely possible to exceed the bandwidth of a link.  I noted that 
with an RF link with a decent baudrate (don't remember the baud) but 
when GPS was turned on along with GLONASS, as more satellites showed up 
it caused what was apparently a buffer overrun.  Well the way that 
manifested IIRC was Float... Fix... then stuttered around and went to 
Float and back because the data was broken up as more satellites added 
enough data to saturate the bandwidth.

Also some UART-USB bridges are also a problem in this regard too. But 
you're probably talking straight through the USB.

So you'd wanna make sure all packet data not used by RTKLIB is turned off.

If you have a battery backup on your NV08C board, you can (and should) 
configure your device with the factory software- including elevation 
mask- and store it, and just move it to RTKLIB to run.


On 11/2/2013 11:47 PM, Neil Schemenauer wrote:
> Hi,
> Before I get into a long description of my problems, I want to thank
> the people making open-source GNSS a possibility.  RTKLIB looks like
> an amazing piece of work, thanks to T. Takasu for such a generous
> gift to the world.  Also thanks to Michele Bavaro, he has been very
> generous with his time as well.
> I purchased two NV08C-CMS receivers from OptimalSystem.DE.  I'm
> using two Tallysman TW3430 antennas.  The hardware seems to be
> working but I have trouble getting a FIX solution.  I think
> something is wrong with my setup but I don't know what.  My view of
> the sky is pretty clear and I think my antennas are pretty good
> quality.  The baseline is short, say 25 to 1000 m.
> Here is one of many different sets of RTKNAVI options that I tried:
>      http://arctrix.com/nas/tmp/rtk-kin2.conf
> I tried AR "fix-and-hold" as well as "continuous".  I tried GPS
> only, GPS+SBAS, GPS+GLO, GPS+GLO+SBAS.  I can often get a FIX
> solution if I use "static" instead of kinematic, if I wait a while.
> Kinematic can't seem to hold a fixed solution.  BTW, can I use
> static if I am occasionally moving the rover while doing a survey?
> The monitor log has errors like:
>      ambiguity validate failed nb=10 ratio=1.23 s=xx/xx
>      large residual (sat=XX-X ...)
> I think the 's' number gets larger as I run RTKNAVI.  I sometimes
> get a FIX solution for a moment when I first start RTKNAVI.  Based
> on the ground track plot, it looks to be the correct fix but it
> switches to FLOAT almost immediately.
> Here are some NVS BINR files I saved from the base station.
>      http://arctrix.com/nas/tmp/roof.zip
>      http://arctrix.com/nas/tmp/roof-20131102.zip
> The RINEX files for the 20131102 data is here if you want to look at
> it directly:
>      http://arctrix.com/nas/tmp/roof-20131102.obs
>      http://arctrix.com/nas/tmp/roof-20131102.nav
> I mounted the antenna on a roof, trying to stay above or away from
> possible multi-path sources.  Maybe I was not entirely successful.
> It seems like RTKLIB doesn't show anything about multi-path, maybe
> due to a limit of the NV08C receiver?
> Here is a PPP solution from the PPP tool provided by Natural
> Resources Canada (uses precise GNSS orbits and clocks).  I'm getting
> horizonal RMS errors of about 0.8 m, even with multiple hour
> observation data.  I was hoping for better.  This is shorter
> observation, from the roof.zip data I think:
>      http://arctrix.com/nas/tmp/roof-ppp.pdf
> In the above report, it looks like the receiver clock has a lot of
> drift, maybe that doesn't matter.
> Another thing I noticed this afternoon while playing with the
> hardware, I don't seem to get many "NAV" messages from the
> receivers.  I understand these contain ephemeris and clock data.
> When I look at the RTKNAVI monitor, the "Obs(x)" count increases
> continuously but for "Nav(x)" I only seem to get a few after
> starting STRSRV.
> That leads me to another question.  Does anyone know where the
> startup/shutdown commands for the NV08C-CMS are documented?  Based
> on the datasheet, I guess these may depend on the firmware loaded on
> the receivers.  It would be nice to know some more details though.
> For example, the Storegis tool allows the elevation mask to be set.
> Maybe that's not relevant if you are reading raw data using BINR
> though.
> I may be on the wrong track since I'm not an expert on GNSS but this
> NAV message issue seems like a problem.   Sometimes RTKNAVI will
> show many GPS sat signals above 40 dB but they will all be grey.
> Sometimes they will stay that way for many minutes.  It seems like
> restarting some of the programs may fix, maybe restarting STRSRV.  I
> think they are shown grey because there is "Obs" data but no "Nav"
> data for them.  The monitor view seems to confirm this.  The
> Storegis has no trouble finding many satellites and the position
> seems very stable so I don't think there is something wrong with my
> antenna, cable, etc.
> Thanks for any direction and thanks again to the people making open
> source GNSS happen.
>    Neil
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